The counterfeiting of luxury (and even non-luxury) goods has become so common that major manufacturers of everything from shoes to Shiraz have started dedicating portions of their websites to telling buyers how to spot real from fake.

Golf club maker Callaway, for example, has an alert on its website telling buyers how not to be fooled by fake clubs. "To protect our valued customers from fraud," it begins, "Callaway golf shares the following warning."

It goes on to say that consumers around the world have been duped into purchasing "so-called brand-new, authentic Callaway Golf products at very low prices" on Internet auction and retail sites "that have turned out to actually be low-quality fakes."

Such fakes, says Callaway, have dramatically increased over the last few years. When a single driver can cost $450 at retail, falling prey to fakes can prove expensive for the deceived consumer.

How do you spot counterfeit clubs? Callaway's website provides some guidelines.

Anything purchased from any seller other than an authorized Callaway Golf retailer, says the site, should be viewed with suspicion. Is the price too good to be true? That, too, should raise an eyebrow.

"Does the seller explain his willingness to part with the clubs at a bargain-basement price by claiming that he 'won the clubs' in a tournament or raffle, or that they were 'a gift' that he doesn't need?" Sellers of fake Callaways often offer such explanations, the site warns.

Some portions of authentic clubs are made of a carbon composite material. If you take a key or coin and tap the section of the club's head that should be composite, and it makes a metallic "ping," it likely is a fake, says Callaway.

If all else fails, the suspicious shopper can always call Callaway to ask if the serial number on the clubs is valid. Alternatively, he or she can take the clubs to an authorized dealer for expert inspection.

Estimates vary on how big a problem fakery is worldwide.

Australian footwear maker UGG, for example, estimates that counterfeiting costs manufacturers $600 billion a year worldwide in lost revenue.

One pair of images on the site shows, side by side, a genuine UGG shoe-box and a counterfeit shoe-box. Reads a warning: "These images illustrate common features you can sometimes spot on counterfeit product. Keep in mind that it's very difficult to identify fake products on websites. Counterfeiters copy our website, from logos to product, images to product descriptions."

Coach's site lists third-party websites authorized to sell Coach products (there are only eight) and warns consumers against buying Coach products elsewhere, even from sites that may have the word "Coach" in their URL or that may have content or layout similar to www.coach.com.

Susan Scafidi, head of the Fashion Law Institute at Fordham Law School, explained earlier this year to The Business Insider how to spot a fake handbag, whether Coach, Gucci, or some other.

Use your sense of touch, she advises. Counterfeits, she says, are intended to fool the eye, not always the fingers.

The leather of an authentic top-quality handbag, experts say, should be dry, not sticky; supple, not stiff.

If you tap the hardware and it's hollow, is it supposed to be? Is the stitching straight? Is the lining the same color as an authentic bags?

When you're paying top dollar for a real Louis Vuitton, you're supposed to be getting flawless workmanship. Does the bag you're handling meet that high standard, or does its maker seem to have cut corners and compromised on quality?

Is there a loose thread? An imperfectly-aligned zipper? According to manufacturers of legit luxyry goods, such flaws should be tip-offs to fakery.

Top-quality products typically are sold with documentation—ID cards, say, attesting to their authenticity, or proof-of-purchase forms to be filled out and submitted by the buyer. If these are missing, view the product with suspicion.

Forbes magazine says even fine wines sometimes have been counterfeited.

Though it's more common, according to Forbes, for rare and costly vintages to be faked—a 1982 Chateau Petrus, say, selling for $3,500 a bottle—even wines retailing for $100 a bottle have been found to be counterfeit.

He shines a light into the bottle: Does the amount of sediment comport with the wine's purported age? He checks the appearance and texture of the glass itself: The technology of making wine bottles has changed over the decades. Modern bottles are seamless. Older ones have seams, distortions, bubbles trapped in the glass. Does the age of the glass match the purported age of the vintage?

Finally, the sommelier checks the ullage—the degree to which the bottle may fall short of being perfectly full. An old bottle, even if it has been well stored, should show some evaporation. If the label says the wine is from 1880 and the bottle is perfectly full, you may be looking at an illustration of the old truism, "in vino falsitas."